Rescue and Recovery Workers responding in the aftermath of the September 11, 2001 World Trade Center (WTC) attacks exhibit elevated rates of multiple morbidities, including post-traumatic stress disorder (PTSD), depression, panic disorder, and respiratory and gastro-esophageal diseases. These physical and mental illnesses are presumed to result from direct exposure to the metals, chemicals, gases, and particles contained within the dust cloud and debris pile at the WTC site coupled with the psychological trauma of witnessing the disaster and participating in its cleanup. Cognitive function, such as short-term memory and ability to concentrate, has not been formally explored within this cohort. Rescue and Recovery Workers may have experienced cognitive decline in the 13 years since the attacks beyond that attributable to the normal aging process through direct and indirect pathways. A direct neurotoxic effect of the WTC disaster on cognitive function could occur because the massive exposure to environmental toxins from the fires and collapse of the towers could directly impair cognitive function. An indirect effect of the WTC disaster on cognitive function could operate through physical and mental comorbidities that were caused by work at the WTC site. Identifying an impact of the WTC disaster on long-term cognitive function and then differentiating between direct and indirect effects can address critical gaps in understanding the health consequences of the attacks. Documenting an association between exposure and cognitive impairment is important to improve identification of those at risk. Understanding the contribution of direct versus indirect effects can facilitate diagnostic and treatment planning. We propose to address this critical gap in knowledge about WTC exposure and cognitive health. Using existing, longitudinal data from the New York City Region Clinical Centers of Excellence we will employ a novel analytic approach to address cognitive function among nearly 25,000 Rescue and Recovery Workers participating in the WTC Health Program. We will (1) quantify the association between WTC exposure and cognitive function; (2) use Structural Equation Models to estimate the direct and indirect effects of WTC exposure on cognitive function; and (3) in exploratory analyses, develop a set of vulnerable traits that identiy Workers at elevated risk of cognitive dysfunction. This proposed study is a responsive, efficient, and cost- effective use of existing data and the first to formally assess cognitive function in Rescue and Recovery Workers. If we determine that cognitive decline results from direct or indirect effects of WTC exposure then interventions could be implemented to improve diagnostic and treatment actions to mitigate loss of function.